As erythromycin ototoxicity appears to be favored by renal insufficiency, its pharmacokinetics were assessed in chronic uremic patients treated by maintenance hemodialysis in comparison with normal subjects. Two groups of 8 patients each were studied, the first one on an interdialytic day, the second immediately after the end of an hemodialysis session. All subjects ingested a single dose of 1 gram of erythromycin ethylsuccinate. Times of peak serum concentration and biological half-lifes were similar in patients and in controls. Maximum serum concentrations and areas under the serum concentration time-curve were higher in patients than in controls whereas apparent oral clearances were lower in the former. The differences between the two groups of patients were not significant. These pharmacokinetic changes are suggestive of an enhanced bioavailability of erythromycin in chronic renal failure which might predispose uremics to the ototoxicity of the drug.